Anode Active Material Particles Encapsulated in Pyrogenic, Nanostructured Metal Oxides and Methods of Making and Using the Same

The invention relates to a method of producing encapsulated anode active material particles in which carbon and/or Si-based particles and fumed, nanostructured metal oxides are mixed dry under shearing conditions. The invention further relates to the fumed metal oxide coated anode material as well as to a battery cell containing the encapsulated carbon and/or Si-based anode particles and use thereof.

Various energy storage technologies have recently attracted much attention of public and have been a subject of intensive research and development at the industry and in the academia. As energy storage technologies are extended to devices such as cellular phones, camcorders and notebook PCs, and further to electric vehicles, demand for high energy density batteries used as a source of power supply of such devices is increasing. Secondary lithium-ion batteries are one of the most important battery types currently used.

The secondary lithium-ion batteries are usually composed of an anode made of a carbon material or a lithium-metal alloy, a cathode made of a lithium-metal oxide, and an electrolyte in which a lithium salt is dissolved in an organic solvent. The separator of the lithium-ion battery provides the passage of lithium ions between the positive and the negative electrode during the charging and the discharging of the battery.

US2019/0393543 describes a lithium metal secondary battery, comprising a cathode, an anode, and a porous separator or electrolyte disposed between the cathode and the anode, wherein the anode comprises: (a) an anode active layer containing a layer of lithium or lithium alloy, in a form of a foil, coating, or multiple particles aggregated together, as an anode active material; and (b) an anode—protecting layer of a conductive sulfonated elastomer composite, disposed between the anode active layer and the separator/electrolyte.

US201363345 describes forming a protective coating of graphene on a negative lithium metal electrode, for lithium containing electrochemical cells, such as lithium-ion batteries. The graphene protective coating is said to reduce dendrite formation and growth.

WO2019215406A1 describes an anode for a lithium-ion battery, including at least one anode material which is binder-free, is pre-charged with lithium ions, and coated with a protective coating including a very long list of allegedly suitable materials, however none of the coatings employed in the present invention are disclosed in WO2019215406A1.

CN106025242A describes a composite anode material for a lithium-ion battery comprising a core layer of a porous silicon alloy nanowire with carbon nanotubes and a shell layer made of a conductive polymer film of a polypropylene oxide, polyethylene succinate, polyethylene succinate, or polyethylene glycol imine blended with graphene.

The coating of cathode materials of lithium-ion batteries with AlO, TiO, ZrOfor improving their cycling performance, is known.

Examples of use of metal oxide in cathode materials are provided in the following articles. In the article “mesoporous carbon material as cathode for high performance lithium-ion capacitor” published in Chinese Chemical Letters (2018), 29 (4) 620-623, by Zhang et al. Mg citrate was used as the precursor of the C mesoporous and the nano-sized metal oxide particles as template provided by the Mg citrate.

In the article “Improvement of cycling performance of lithium-sulfur batteries by using metal oxide as a functional additive for trapping lithium polysulfide” of Ponraj et al. published in ACS Applied Material Interfaces 2016, 8, 4000-4006, hydrophilic metal oxide was used as an additive on the surface of the active sulfur of positive electrodes to trap polysulfides.

Elements like carbon and its allotropes (graphene) have been used as anode materials in lithium-ion secondary batteries, however, there exist several issues with the structural stability of the graphene in the anode. In the article “An electrode comprising of graphene nano-powder inserted in an enclosed structure in anodic aluminum oxide coated with PANI by using low temperature hydrothermal process” of Sugam et al. published in 1942, 62nd DAE Solid State Physics Symposium, 2017, graphene nano-powder was inserted and confined on an anodic aluminum oxide coated using PANI (polyaniline).

In the article “An alumina-coated Fe3O4-Reduced graphene oxide composite electrode as a stable anode for lithium-ion battery” of Qi-Hui et al. published in Electrochimica Acta 2015, 156, 147-153, an AlOcoating was used on a FeO-reduced graphene oxide composite anodic material.

CN 104 393 258 discloses oxide coated Si titanium alloy (graphene nanocomposite materials.

Wu Xing et al. describe in “Electrochemical studies of MgFeO@TiOcore-shell nanospheres as anode material for lithium battery applications” in Journal of Materials Science: Science in Electronics, vol. 29, no. 20 (2018), pages 17872-17880, ISSN: 0957-4522, a one-step hydrothermal method to produce core-shell-structures based on MgFeOand TiO.

A rather major general problem with anode materials, especially silicon-based anode materials, is the uncontrolled solid electrolyte interface (SEI) formation during initial charge-discharge processes of a battery. In addition, aging processes within the bulk of the material result in the loss of performance during cycling. This aging phenomenon is especially relevant for Si based anode active materials. During cycling the negative electrode material suffers from several electrochemical degradation mechanisms that may cause deactivation of the negative electrode material. Electrolyte induced surface transformations and unwanted side reactions with lithium species lead to the formation of SEI layers with increased thickness, finally resulting in a decreased performance and battery lifetime.

Surface coating has proven to be an extremely important method to address this aging problem by suppressing the direct contact between the active materials surfaces and the liquid electrolyte.

Although nano-sized metal oxide particles have been used as additives in lithium-ion batteries their effectiveness has been limited by poor dispersibility. Hence, practical ways to improve the long life of secondary lithium-ion batteries are often limited. Often times, the use of commercially available nano-sized metal oxides leads to inhomogeneous distribution and large agglomerated metal oxide particles on the surface of the anode materials. As a result, the anode material particles are not fully covered by the metal oxide particles and large non-dispersed metal oxide particles are present, located next to the anode particles, and are clearly visible by SEM elemental mapping.

The problem addressed by the present invention is that of providing a homogeneous coating layer of a metal oxide or a mixture of metal oxides around an anode active material comprising carbon and/or Si-based particles.

In the course of thorough experimentation, it was surprisingly found that pyrogenically produced, nanostructured metal oxide of alumina or titania (or mixed metal oxides of alumina and titania) may successfully be used for coating of anode materials including carbon and/or Si-based particles using a dry mixing process for coating the metal oxide on the anode materials. It was also surprisingly found that further surface modification of the pyrogenically produced, nanostructured metal oxide prior to the dry mixing may further improve the coverage and homogeneity of the coating significantly.

The invention provides a process for producing a coated active anode material, the coated active anode material, and the use of the coated active anode material in a lithium-ion battery. The lithium-ion battery of the present invention can be used in electronic and electric apparatuses including, for example, mobile phones, computers (lap top computers, desk top computers, computer pads), electronic watches, key fabs, electric appliances, power tools, vacuum cleaners, electric lawn mowers and electric vehicles.

According to a first aspect of the present invention there is provided a process for producing a coated active anode material. The process is characterized in that the coated active anode material is obtained by subjecting an active anode material and a pyrogenically produced metal oxide of alumina or titania to dry mixing in a mixing unit under shearing conditions, characterized in that the coated active anode material is in the form of particles, and the metal oxide has a BET surface area of 5-300 m/g, a mono-modally and a narrow particle size distribution with a mean aggregate diameter dof 5-150 nm, as determined by static light scattering (SLS) after 60 seconds of ultrasonic treatment at 25° C. of a mixture consisting of 5% by weight of the particles and 95% by weight of a 0.5 g/L solution of sodium pyrophosphate in water.

The pyrogenically produced metal oxide is hydrophilic. Preferably, in an embodiment, the pyrogenically produced metal oxide is subjected to a surface modification to become hydrophobic.

In an embodiment, the mixing unit has a specific electrical power of 0.05-1.5 KW per kg of the mixed anode material.

The coated active anode material is in the form of particles, and the metal oxide has a BET surface area of 5-300 m/g, a mono-modally and narrow particle size distribution with a mean aggregate diameter dof 5-150 nm, more preferably 10-120 nm, even more preferably 20-100 nm, as determined by static light scattering (SLS) after 60 seconds of ultrasonic treatment at 25° C. of a mixture consisting of 5% by weight of the particles and 95% by weight of a 0.5 g/L solution of sodium pyrophosphate in water.

SEM-EDX mapping of the coated active anode material provides a fully and homogeneous coverage of the metal oxide substantially around all anode particles, with no or only few larger metal oxide agglomerates.

In an embodiment, the process is characterized in that the specific electrical power of the mixing unit is 0.1-1000 KW, the volume of the mixing unit is 0.1 L to 2.5 m, and the speed of a mixing tool in the mixing unit is 5-30 m/s.

The span (d-d)/dof particles of the metal oxide and/or of the mixed oxide comprising aluminum or titanium is 0.4-1.2, as determined by static light scattering (SLS) after 60 seconds of ultrasonic treatment at 25° C. of a mixture consisting of 5% by weight of the particles and 95% by weight of a 0.5 g/L solution of sodium pyrophosphate in water.

In an embodiment, the active anode material is in the form of powder and comprises carbon particles, silicon particles, or silicon oxide particles or any combinations thereof.

The active anode material comprises carbon and/or Si-based particles. Si-based particles as this term is used herein means silicon particles (e.g., pure silicon particles), silicon oxide (SiOx) particles, and any combinations of silicon, silicon oxide, and carbon particles including mixtures and composites thereof. Silicon oxide can be SiO and/or SiO.

In an embodiment, the coated active anode material is further subjected to a heat treatment following the dry mixing.

In an embodiment, the proportion of the metal oxide in the coated active anode material is 0.05%-5% by weight, based on the total weight of the coated mixed anode material.

Another aspect of the present invention is directed to the coated active anode material obtainable by the above process.

According to yet another aspect of the present invention there is provided a coated active anode material comprising an active anode material and a coating of a pyrogenically produced, nanostructured metal oxide on the surface of the mixed anode material, wherein the coated active anode material is in the form of particles, and the metal oxide has a BET surface area of 5-300 m/g, a mono-modally and a narrow particle size distribution with a mean aggregate diameter dof 5-150 nm, as determined by static light scattering (SLS) after 60 seconds of ultrasonic treatment at 25° C. of a mixture consisting of 5% by weight of the particles and 95% by weight of a 0.5 g/L solution of sodium pyrophosphate in water and wherein the pyrogenically produced, nanostructured metal oxide is preferably surface treated to become hydrophobic may by reacting the hydroxyl groups of alumina or titania with a silane to form —O—Si—R groups. The metal oxide is hydrophilic or hydrophobic, preferably hydrophobic. The active anode material is carbon, silicon, silicon oxide (SiOx), or any combinations thereof, including mixtures and/or composites of carbon, silicon, and silicon oxide.

Other aspects of the present invention, are directed to an active negative electrode material for a lithium-ion battery comprising the coated active anode material, also to a lithium-ion battery comprising the coated active anode material, and also to the use of the coated active anode material in an active negative electrode material of a lithium-ion battery.

Yet another aspect of the present invention is directed to an apparatus powered by the lithium-ion battery.

The nanostructured metal oxide made by the flame process has a mono-modally and narrow particle size distribution in combination with an excellent dispersibility during the dry coating process of the anode material. These particles lead to an excellent interaction and proper adhesion to the anode active material.

Furthermore, the additional surface modification of these particles leads to further improvements in interaction and adhesion to the anode active material. This results in a complete de-agglomeration of the metal oxide agglomerates and finally provide a fully and homogenously covered anode active material particles by fumed, nanostructured and surface modified metal oxide.

It has been found that by using a high intensity dry coating process in combination with the pyrogenic, nanostructured metal oxide particles, the present invention method results in significantly improved dispersibility of the metal oxide particles and homogeneous coating. During the dry mixing the applied shear forces (mixing) decompose any metal oxide agglomerates into tiny aggregates which have a very high tendency to settle down on the surface of the anode active material particles powder resulting in very good interaction and adhesion which in turn results in a homogeneous coating. In contrast, conventional metal oxide particles, which are not pyrogenically produced and nanostructured, are composed of isolated, spherical particles (which are the result of milling coarser metal oxide particles) and do not show such behaviour.

These and other features and advantages of the invention will become better understood from the following detailed description in conjunction with the following figures.

According to a first aspect of the invention there is provided a method of producing encapsulated active anode material particles in which an active anode material and fumed, nanostructured metal oxide are mixed dry under shearing conditions. The fumed, nanostructured metal oxide is preferably also surface modified to become hydrophobic prior to the dry mixing. A second aspect of the invention relates to the fumed metal oxide coated anode material, and a third aspect of the invention relates to a battery cell containing the encapsulated carbon and/or Si-based anode particles.

According to a first aspect of the present invention, there is provided a process for producing a coated active anode material, wherein active anode material particles such as carbon, and/or Si-based anode particles and a pyrogenically produced, nanostructured, and/or a pyrogenically produced mixed oxide comprising at least two metals are subjected to dry mixing under shearing conditions. Si-based anode particles includes silicon particles, silicon oxide particles, and any combinations of silicon, silicon oxide, and carbon particles.

The fumed, nanostructured metal oxide is preferably also surface modified to become hydrophobic prior to the dry mixing.

The active anode material may be referred to also as the core active anode material or the substrate active anode material or particles. The pyrogenically produced, nanostructured and, preferably, surface modified metal oxide may also be referred as the coating. The coated active anode material refers to the mixed active anode material with the coating produced by dry mixing. Once the dry mixing is completed the carbon and/or Si-based particles are covered with said metal oxide.

Dry mixing may be performed, for example, in a mixing unit having a specific electrical power of 0.05-1.5 KW per kg of the mixed anode material. Dry mixing is understood to mean that no liquid is added or used during the mixing process, that is e.g., substantially dry powders are mixed together. However, it is possible that there are trace amounts of moisture or some other than water liquids present in the mixed feedstocks or that these include crystallization water.

If the used specific electrical power is less than 0.05 KW per kg of the mixed anode material, this gives an inhomogeneous distribution of the metal oxide on top of the anode active material particles, which may be not firmly bonded to the core material of the anode active material particles. A specific electrical power of more than 1.5 KW per kg of the mixed anode material leads to poorer electrochemical properties. In addition, there is the risk that the coating will become brittle and prone to fracture. The nominal electrical power of the mixing unit can vary in a wide range, e.g., from 0.1 kW to 1000 kW. Thus, it is possible to use mixing units on the laboratory scale with a nominal power of 0.1-5 KW or mixing units for the production scale with a nominal electrical power of 10-1000 KW. The nominal electrical power is the nameplate, maximal absolute electrical power of the mixing unit.

The volume of the mixing unit may vary in a wide range. For example, the volume of the mixing unit may range from 0.1 L to 2.5 m. For example, mixing units on a laboratory scale may have a volume of 0.1-10 L or mixing units for the production scale may have a volume of 0.1-2.5 m.

Preferably, in the process according to the invention, forced action mixers are used in the form of intensive mixers with high-speed mixing tools. It has been found that a speed of the mixing tool of 5-30 m/s, more preferably of 10-25 m/s, gives the best results. Examples of commercially available mixing units which are suitable for the process of the invention include Henschel mixers and Eirich mixers. The Eirich mixers may be, for example, high intensity Eirich mixers.

The mixing time may vary and may be preferably from 0.1 to 120 minutes, more preferably from 0.2 to 60 minutes, and most preferably from 0.5 to 10 minutes.

The mixing may be followed by a thermal treatment of the mixture for improved binding of the coating to the anode active material particles. However, this treatment is optional in the process according to the invention since in this process, the pyrogenically produced, nanostructured and surface modified metal oxide adheres with sufficient firmness to the core anode active material particles, i.e., the carbon and/or Si-based particles. Hence, a preferred embodiment of the process according to the invention may not include a thermal treatment after the mixing.

It has been found that the best results regarding the adhesion of the metal oxides to the core anode active material particles are obtained when the metal oxide has a BET surface area of 5 m/g-300 m/g, more preferably of 10 m/g-200 m/g and most preferably of 15-150 m/g. The BET surface area can be determined according to DIN 9277:2014 by nitrogen adsorption according to the Brunauer-Emmett-Teller procedure.